The proposed work deals with several aspects of the molybdenum cofactor. 1) Investigation on the structure of the novel pterin component of the cofactor will be continued. 2) Studies on the biosynthesis of the cofactor pterin will be initiated, using E. coli. To this end, attempts will be made to obtain and characterize mutants deficient in cofactor. 3) Procedures for the isolation of active cofactor will be formulated, and the structure of the active material will be examined. 4) The possible existence of cofactor mutants in Drosophila melanogaster will be examined, since Drosophila is a viable system for biosynthetic studies.